Nothing like that. DS flash carts are mostly used for NDS roms. I was thinking of using it as more than just a mere flash cart for NDS roms, more like a secondary microSD card slot.For what reason do you ask? Are you trying to play NDS roms on your flash cart?
Basically, it could be used as another place for 3DSX homebrew, CIA files, etc.
The idea came from DS-Mode being able to read the original R4 directly, and ahezard's nds-hb-menu (running in DSi-Mode) now being able to switch between the SD card, and the original R4 by pressing START/SELECT. Would be neat if smea's and mashers' HBL switches between them as well.